Solvent containing adhesives are most commonly used in tire manufacture because they are easy to work, especially at low temperature, and generally provide a good quick bonding capacity and good adhesive strengths. A serious disadvantage of solvent containing adhesives is the large quantity of organic solvents they contain. The latter are released by evaporation during working and thus result in a considerable odor nuisance which, in some circumstances, may even lead to a health risk for the person working with said adhesive. An additional point to note when working with these adhesives is that, owing to the evaporation, explosive solvent/air mixtures may be produced. In view of the hazards associated with the use of organic solvents, it would be desirable to eliminate the amount of organic solvent present in adhesive compositions which are used for bonding, for example, tread stock to a carcass portion during the building of a tire.
Aqueous compositions have been used prior to the present invention for bonding polyester tire cords to rubber compounds. For example, U.S. Pat. No. 2,482,931 to Perkerson provides a method of bonding rubber to cotton and rayon fabrics for the production of tire carcasses by employing an adhesive comprising a rubber latex and a small amount of a water-soluble salt of polyacrylic or polymethacrylic acid. There is no disclosure of bonding tread stock to a tire carcass.
U.S. Pat. No. 3,843,484 to Kamiyoshi et al describes a method for bonding a synthetic fibrous material to rubber by applying an aqueous dispersion containing a novolak resin which is derived from the reaction of a monohydroxy benzene and formaldehyde, a precondensate derived from the reaction of resorcinol and formaldehyde and a rubber latex.
U.S. Pat. No. 3,857,730 to Kalafus et al. describes a process for bonding rubber compounds to polyester reinforcing elements by employing a one-step dip process in which the dip consists essentially of an alkaline aqueous emulsion of a rubbery vinyl pyridine copolymer containing butadiene-styrene and 2-vinyl pyridine and a heat reactable 2,6-bis(2,4-dihydroxy phenylmethyl)4-chlorophenol composition.
U.S. Pat. No. 3,947,394 to Kalafus et al. provides a process for bonding rubber compounds to polyester reinforcing elements, particularly tire cords of polyester fibers, using a one-step dip process in which the dip consists essentially of an alkaline aqueous emulsion of a minor amount by weight of a mixture of a major amount by weight of a rubbery vinyl pyridine copolymer and a minor amount by weight of a heat reactable 2,6-bis(2,4-dihydroxy phenylmethyl)-4-chlorophenol composition, wherein said emulsion is essentially free of alkali metal materials and wherein the emulsifier used in the emulsion is an ammonium salt or soap. High aged H-adhesions are obtained with this process.
U.S. Pat. No. 4,026,744 to Elmer also discloses a method for bonding rubber compounds to reinforcing elements by using a dip process in which the dip contains an alkaline aqueous dispersion of a mixture of a rubbery vinyl pyridine/styrene/butadiene terpolymer and a lignin sulfonate-resorcinol-formaldehyde reaction product.
U.S. Pat. No. 4,285,756 to Elmer describes an aqueous alkaline dispersion containing a rubbery polybutadiene and a water-soluble heat reactive phenolic resin which is useful as an adhesive for bonding polyamide or polyester reinforcing elements to ethylene-propylene-diene rubbery polymer compounds.
U.S. Pat. No. 4,440,881 to Girgis provides an aqueous coating composition for filamentary materials, which composition yields coated filamentary material with improved weavability and that yields reinforced elastomeric materials having improved properties of flexibility and fatigue resistance. The aqueous adhesive coating composition has a vinyl-pyridine-containing copolymer or terpolymer latex, a non-selfcrosslinkable elastomeric latex, a carboxylated butadiene polymer, and a phenolic aldehyde condensate polymer. The vinyl pyridine-containing elastomeric latex is produced from a vinyl pyridine-containing monomer, 1,3-diene hydrocarbon monomer or the terpolymer is produced in the same way with the addition of a vinyl containing monomer. The non-selfcrosslinkable elastomeric latex has a low gel content of less than around 40 weight percent and a low average particle size of less than around 2000 angstroms. The carboxylated butadiene polymer or butadiene styrene copolymer has less than 75 percent bound styrene and about 1 to 10 weight percent carboxylation, where both values are based on the weight of the carboxylated polymer or copolymer. The amount of the carboxylated butadiene polymer or butadiene styrene copolymer in the coating is in the range of 3 to about 10 weight percent on the basis of a dried coating. In addition, the aqueous adhesive coating composition may contain a wax emulsion, and antioxidant. The aqueous adhesive coating composition is used to treat filamentary material, which are then dried or dried and partially cured, and combined with the elastomeric matrix material to produce reinforced elastomeric products.
U.S. Pat. No. 4,463,120 ("the '120 patent") discloses a process for preparing an aqueous adhesive composition which comprises preparing a solvent dispersion by mixing rubber, carbon black, vulcanizing agent, tackifying resin and accelerator with sufficient organic solvent to form a solvent dispersion and thereafter emulsifying the solvent dispersion in the presence of water to form an aqueous emulsion. The aqueous emulsion may be used to bond unvulcanized rubber compounds, such as a tread stock to the carcass portion during the formation of a tire. While the '120 patent utilizes organic solvents, the present invention achieves better adhesion without the use of the environmentally deleterious organic solvents.
U.S. Pat. No. 4,497,927 ("the '927 patent") discloses a tire tread adhesive or cement having superior green tack, excellent cured adhesion, and rapid drying time is disclosed. The tread cement comprises a water-in-oil emulsion having an oil continuous phase in which is dissolved a vulcanizable rubber compound. The water-in-oil emulsion tread adhesive may contain from 20-80% water, thereby minimizing environmental contamination on drying. Again, while the amount of organic solvent is minimized, organic solvents continue to be present in the compositions of the '927 patent.
U.S. Pat. No. 4,623,414 ("the '414 patent") discloses a process for preparing an aqueous adhesive composition which comprises preparing a solvent dispersion by mixing rubber, carbon black, vulcanizing agent, tackifying resin and accelerator with sufficient organic solvent to form a solvent dispersion and thereafter emulsifying the solvent dispersion in the presence of water to form an aqueous emulsion. The aqueous emulsion may be used to bond unvulcanized rubber compounds, such as a tread stock to the carcass portion during the formation of a tire. The '414 patent is a based on a divisional application from the '120 patent and thus comprises the same drawbacks as the '120 patent.
The above listed patent documents are hereby incorporated by reference herein.
Although the above references disclose aqueous compositions for bonding reinforcing elements such as tire cords to rubber compounds, these references do not describe compositions which are completely devoid of organic solvents, while at the same time displaying superior adhesive properties equivalent to those shown by the compositions of the present invention.